The present invention relates to non-gelling high polymer compositions. The present invention also relates to polymer blend compositions which contain non-gelling, high molecular weight polymer compositions and thermoplastic polymer resins. The present invention further relates to processes for increasing the melt strength of thermoplastic polymer resins using non-gelling, high molecular weight polymer compositions. The present invention even further relates to processes for preparing non-gelling, high molecular weight polymer compositions and polymer blend compositions containing the same.
Thermoplastic polymer resins are used to prepare numerous articles of commerce. Similarly, there are many polymer melt processing methods used for fashioning articles from thermoplastic polymer resins.
While certain polymer melt processing methods require molten polymer resins that are fluid in nature and flow readily, other polymer melt processing methods require molten polymer resins that resist flow. Such molten polymer resins that resist flow are deemed to have a high melt strength.
While many thermoplastic resins have sufficient melt strength, others such as polyolefins (e.g., polypropylene and polyethylene) typically do not. Those thermoplastic resins which have relatively lower melt strengths tend to sag when the requisite heat and stress necessary to melt and mold them during certain processing procedures. Sagging of molten thermoplastic resins is especially a problem during molding processes which involve thick and heavy articles. These problems can result in the articles being formed having breaks, cracks and/or varying thicknesses. Accordingly, the plastic processing industry has continually sought to increase the melt strength of certain thermoplastic resins.
There have been several attempts to resolve this melt strength problem. One such attempt is disclosed in U.S. Pat. No. 5,506,307 (“Memon”).
Memon discloses increasing the melt strength of a polyolefin by the addition of additives based on high molecular weight polymers. Specifically, Memon discloses that high molecular weight polymers and certain copolymers of C10 to C30 alkyl (meth)acrylates can be used to increase the melt strength of polyolefins. Memon also discloses that such additives can be a homopolymer of one or more C10 to C30 alkyl (meth)acrylate or a copolymer containing at least 70 weight percent of the one or more C10 to C30 ester of an alkyl (meth)acrylate with up to 30 weight percent of one or more of a C1 to C9 alkyl (meth)acrylate, the homopolymer or copolymer having a weight-average molecular weight of at least 670,000, more preferably at least 1,500,000.
Memon recognized that it is difficult to polymerize monomers such as the higher alkyl (meth)acrylates, which are almost completely insoluble in water, with conventional amounts of emulsifiers and those conventional initiators which are effective for lower alkyl alkyl (meth)acrylate monomers, such as ethyl acrylate or methyl methacrylte. Memon further recognized that problems commonly encountered during such emulsion polymerizations can include: poor conversion to polymer, puddling of monomer with resultant gum, phase separation of particles, and non-uniform copolymerization in the presence of monomers having higher water solubility. While Memon alleviated many of the aforementioned problems, the plastics industry continues to seek further improvements in this area.
It is known in the plastics' industry that high-alkyl (C8 to C30) (meth)acrylate polymers oftentimes contain gelled polymer chains. Under certain circumstances, this is undesirable. For example, when used as melt strength additives for thermoplastic polymer resins, the presence of gelled polymer chains not only reduces the additive's ability to effectively increase the resulting blend's melt strength, but also reduces the additive's ability to effectively disperse within the blend. Moreover, in addition to reducing its effectiveness as a melt strength enhancer, the poor dispersion of these additives in the resulting thermoplastic resin blend can also cause unattractive optical and surface imperfections in articles being formed.
In view of the above, the plastics' industry would greatly welcome a means for improving the melt strength of certain thremoplastic resins without encountering the problems associated with the formation of gelled polymer chains.
Accordingly, one object of the present invention is to provide a means for improving the melt strength of certain thermoplastic resins without encountering the problems associated with the formation of gelled polymer chains.
Another object of the present invention is to provide a high molecular weight, high-alkyl (meth)acrylate polymer composition which can be used to improve the melt strength of certain thermoplastic resins without encountering the problems associated with the formation of gelled polymer chains.